The lumen is the interior of a vessel within the body, such as the small central space in an artery or vein, or any of their relating vessels, down which blood flows. An aneurysm is a localized dilation of an artery that eventually becomes larger and ruptures. Most aneurysms occur in the main artery of the body such as Abdominal Aortic Aneurysms (AAAs) or Thoracic Aortic Aneurysms (TAAs). AAA is a common disease that is associated with significant mortality if left untreated. A limiting factor to open repair is the patient's physiological suitability to survive the procedure with acceptable risks. While low morbidity and mortality with open AAA repair is reported, patients with associated comorbidities such as cardiovascular or pulmonary conditions may be at an increased risk with surgical repair. The need to better serve these high-risk patients led to the development of endovascular approaches to treat AAA. Endovascular AAA repair involves minimally invasive, transfemoral delivery of a covered stent within the aneurysm, thereby effectively excluding the aneurysm from circulation.
Many patients for whom endovascular AAA repair could potentially be of benefit do not qualify because of anatomic considerations. The primary anatomic reason for exclusion is the presence of a short proximal neck length. A neck length of 15 mm or greater has been considered essential for proper fixation and sealing for stent-grafts. Currently, the vast majority of patients with short neck AAAs are treated by surgical repair.
Thoracic aneurysms may occur in the ascending aorta, the aortic arch, or the descending thoracic aorta. Descending TAA are much easier to access and treat than other manifestations of the disease. Many of the characteristics that are common in AAA are also present in TAA. The cumulative risk of rupturing a TAA is related to aneurysm diameter. The treatment of descending TAA is an ongoing study. According to one study, the placement of endoluminal stent-grafts to exclude the dissected or ruptured site of thoracic aortic aneurysms is a technically feasible and relatively safe procedure.
The replacement aortic valve needs to be secured at the root of the aorta, across the annulus of the existing valve. The typical annulus diameter can exhibit many of the same characteristics as an aorta with an aneurysm (anatomic variability, calcification, presence of diseased tissue). Like AAA stent-grafting, both fixation and seal are essential in aortic valve replacement surgery
Migration and leakage of a stent-graft after apparently successful endovascular repair raises concerns about the long-term durability of endovascular repair. Leaks from fabric tears or between modular systems that permit continued and expansion of the aneurysmal sac can also lead to rupture. The occurrence of migration or leakage requires re-intervention, mostly by insertion of a proximal extender cuff. Endoleaks may persist in 10-15% of patients while late endoleaks may develop in another 5-10% of patients.
A need for delivery of endoluminal reactants has proved to be a vital step in successfully addressing endoleaks and stent migration has generated much activity in solving these issues.
Recent attempts in resolving stent-graft migration and fixation issues have emerged in various forms. In one attempt a graft apparatus further has a plurality of light degradable polymer outer packets containing a tissue adhesive, which is released by fiber-optic scope after the graft is implanted. Expandable foam cuffs surround the middle portion of the graft to promote clotting within the aneurysm sac. The drawbacks to this effort are in a lack of control of the adhesive release, where the light degradable polymer packets are dependent on the light intensity and the light sours proximity to the packets. Further, in situations with high numbers of packets, the release time may become very lengthy.
In another attempt, a self-expandable stent in the form of wires used anchors, including barbs, hooks, or pins were used as a fixation device. However, this effort left unresolved the sealing of the device.
In another attempt, a sealing layer conforms to the interface region between the outer wall of the tubular prosthesis and the inner wall of the body lumen. The sealing layer expanded in situ in order to conform to the geometry of the interface region. The material was partially hardened after introduction to the target location within the body lumen and in situ expansion of the tubular prosthesis body. This device has limits in providing reactants to the body lumen.
In another effort, a sealing element was secured to the outer surface of a tubular member. The tubular member was expandable to engage an endolumenal wall. The sealing element occluded flow around the tubular member between the outer surface and the endolumenal wall. Anchors were used to secure the tubular member to the endolumenal wall, as the seal member was positioned to protect against flow through leakage paths formed at localized areas of deformation in the tubular wall adjacent to the anchors. This device has limits in providing reactants to the body lumen.
In all these attempts, a need still exists to deliver a variety of reactants to an endoluminal prosthesis independently or simultaneously according to precise timing and positioning. Additionally, the need further requires a device that is flexible enough to conform to the many different anatomical presentations of AAAs, TAAs & the aortic valve annulus. A desirable device must be fixed to the wall of the aorta or aortic valve annulus after the physician has found the optimal location for the device, where fixation after location is a key aspect. Such a device must fully seal the proximal end of the graft to prevent endoleaks and perivalvular leaks, and achieve a degree of fixation that will prevent subsequent device migration or dislodgement. Accordingly, there is a need to develop an endoluminal delivery system to overcome the current shortcomings in the art.